McDermott was born in Waterbury, Connecticut, the son of Diane and Richard McDermott. He is of Italian (from his maternal grandfather), Irish, English, and French descent. Diane was 15 and Richard was 17 when McDermott was born; by 1967, the couple had divorced, and Diane and her two children were living with her mother, Avis (Rogers) Marino. On February 9, 1967, Diane was killed. Her death was originally ruled an accident, but police later claimed that evidence they had found would be enough to file murder charges against John Sponza, who had been living with Diane at the time. Sponza told authorities that Diane accidentally shot herself after picking up a gun he had been cleaning. Sponza, who police say had ties to organized crime, was killed in 1972; his body was found in the trunk of a car in a Waltham, Massachusetts, grocery store parking lot.
McDermott and his sister were raised by Avis in Waterbury. As a teenager, he began taking trips to visit his father, who owned the West Fourth Street Saloon in Greenwich Village, New York. The two would go to the movies and the younger McDermott would work in his father's bar, serving drinks and breaking up fights. He would also fast-talk his way into the Mudd Club and Studio 54. McDermott was uncomfortable with himself as a teenager, saying he had a "Dorothy Hamill hairdo". He began to imitate his acting heroes, such as Marlon Brando and Humphrey Bogart, to adopt their demeanor. McDermott graduated from Holy Cross High School in Waterbury.
McDermott's father's third wife was playwright Eve Ensler (author of The Vagina Monologues), who legally adopted McDermott when he was 15 and she was 23. She has since divorced his father. Ensler, with whom McDermott has remained close, encouraged him to pursue an acting career, and began writing roles for him into her plays. After Ensler suffered a miscarriage, he took on the name Dylan, the name planned for her unborn child. He attended acting school at the Jesuit-run Fordham University, as well as studying under Sanford Meisner at the Neighborhood Playhouse School of the Theatre in New York City.
McDermott starred as Chris in the 1989 film Twister about a man who tried to rescue his girlfriend and daughter from a tornado storm. The same year brought Neon Empire, a movie about the rise and fall of one man in Las Vegas. However, his first big break as an actor was in the hit film In the Line of Fire. Through his connection with Clint Eastwood, McDermott was able to land his first major gig in The Practice. The show expanded McDermott's stardom, and he made People's list of the "50 Most Beautiful People In The World 1998" with the magazine calling him "a prime-time heartthrob". He got this distinction again in 2000. Despite his success on The Practice, McDermott was cut from the show. Executive producer David E. Kelley cited "economic and creative realities" as a result of pressure from ABC to reduce costs. McDermott did appear in the final two episodes of the final season.
In 2004, McDermott starred alongside Julianna Margulies four-part mini-series The Grid, playing FBI Special Agent Max Canary in an anti-terrorist unit. Returning to theater in 2006, the actor played a returned soldier suffering from post traumatic stress disorder in the Ensler's play The Treatment. In 2007, McDermott starred in the television series Big Shots. Due to low viewership, the show was canceled in January 2008 after 11 episodes without completing the planned 13-episode season. On October 30, 2008, TV Guide reported that McDermott was due to co-star alongside Shannen Doherty in the film Burning Palms, a satire based on Los Angeles stereotypes told through five intertwining storylines. Beginning in 2009, McDermott starred in the TNT drama Dark Blue, playing a veteran cop who heads a squad of undercover LAPD officers. The show ran for two seasons, each consisting of ten episodes. In 2011, McDermott starred on American Horror Story on FX as Ben Harmon, a cheating husband. He returned to the second season as a new character due to the series' anthology format, this time portraying Johnny Morgan. In 2012, he appeared in three films; The Campaign, playing Tim Wattley, a campaign manager, The Perks of Being a Wallflower, as the father of main character Charlie (Logan Lerman), and Nobody Walks, as Leroy. He recently appeared in the action thriller Olympus Has Fallen as a treacherous Secret Service Agent who helps a group of terrorists seize control of the White House.
In May 2013, McDermott launched his first Photography Exhibition in Montreal, Quebec at Avenue Art Gallery as part of a collaboration with Art Agent, Marina Cutler. The Exhibition titled THE DYLAN PROJECT, MAKE SOME NOISE! tied his support for The V-Day Organization and love of photography together as the project is a way to bring attention and funds to this organization that supports women in various ways who have suffered violent acts of aggression. McDermott and Cutler have plans to bring THE DYLAN PROJECT to other locations. Also in 2013, McDermott starred in the short-lived CBS television series Hostages as FBI agent Duncan Carlisle. In 2014, McDermott began starring on another short-lived CBS television series Stalker in one of the lead roles, portraying Detective Jack Larsen opposite Maggie Q.
McDermott has a younger sister, Robin. He married actress Shiva Rose on November 19, 1995. They have two daughters, Colette and Charlotte. Colette's birth is prominently featured in Ensler's The Vagina Monologues. On September 27, 2007, People confirmed that McDermott and Rose had separated. On May 16, 2008, CelebTV.com reported that McDermott had filed for divorce from Rose. The divorce was finalized on January 2, 2009. On January 14, 2015, it was announced he was engaged to his Stalker co-star Maggie Q.
McDermott has been featured in magazines such as Men's Health. In 1999, he was a finalist in the GQ "Man of the Year" issue. McDermott is a recovering alcoholic who has been sober for over 20 years.Golden Boy
Believe It, See It, Survival (1978)
Biloxi Blues (1985) – Joseph Wyzykowski
Floating Rhoda and the Glue Man (1995)
The Treatment (2006) – Man
Three Changes (2008) – Nate